Trans-alkenoic acids possess hepatoprotective activity comparable to/better than know formulations. Herbal preparations in use as antihepatotoxic/hepatoprotectives are non-standard both from biological and chemical aspects. The first report about natural occurrence of an acid of this type viz, trans-tetracos-15-enoic acid [Wang Huiying, Yu Xuetian, Yi Yuanfen & Ding Jingksi, Yuman Zhiwu Yanjiu, 1989, 11 (1), 60-4 (Ch)] as a constituent of Jojoba oil ex Simmondsia chinensis seeds (0.62-1.11%) was based on GLC analysis.
Both nervonic acid from the brain cerebrosides of cattle and man [Klenk, L. Physiol Chem. 1925, 145,244; 1926, 157, 283; 1927, 166, 268] and selacholeic acid from shark and ray-liver oils [Tsujimoto, J. Soc. Chem. Ind., Japan 1927, 30, 868] were formulated as cis-tetracos-15-enoic acids. The two identical natural products have been synthesized by malonate chain extension of cis-docos-13-enoic acid [J. B. Hale, W. H. Lycan and Roger Adams, J. Am. Chem. Soc., 1930, 52, 4536; Muller & Benzer, Ber., 1939, 72, 615]. In the process tetracos-15-enoic acid was prepared in six steps i.e., (a) Esterification of erucic yield (yield 93%). (b) Reduction of methylerucate with Na metal in n-butyl alcohol (yield 55%), (c) Conversion of erucyl alcohol to erucyl bromide by the action of PBr3 (yield 50%) (d) Condensation of erucyl bromide with malonic ester over a period of forty eight hours (yield 78%). (e) Hydrolysis and decarboxylation of erucyl malonic ester to tetracos-15-enoic acid (yield 50%) (f) Isomerization of cis product to trans form (yield) 90%), in an overall yield of 9.05%.
D. G. Bounds, R. P. Linstead and B. C. L. Weedon, [Journal of Chemical Society, 1954, 448] report synthesis of cis and trans-tetracos-15-enoic acid by anodic chain extension of oleic and claidic acids respectively. This publication discloses the electrolysis of oleic and elaidic acids in presence of excess of methyl hydrogen substrate to give an expected mixture of three products by both symmetrical and unsymmetrial coupling of the two compounds. By distillation and hydrolysis of the unsymmetrical products, mixture of cis and trans-tetracos-15-enoic acids was obtained in 30-35% overall yield.
All the reported synthetic procedures for trans-alkenoic acids till date are lengthy, non-specific i.e., yielding mixture of cis and trans isomers and end up with very poor yields.